Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $26.68   11.760%   $29.8176   $29.82   $29.80   $29.80  
  Purchase #2 $197.61   4.482%   $206.4669   $206.47   $206.45   $206.50  
  Purchase #3 $159.53   13.713%   $181.4063   $181.41   $181.40   $181.40  
  Purchase #4 $236.63   12.240%   $265.5935   $265.59   $265.60   $265.60  
  Purchase #5 $56.97   13.141%   $64.4564   $64.46   $64.45   $64.50  
  Purchase #6 $191.60   6.393%   $203.849   $203.85   $203.85   $203.80  
  Purchase #7 $35.75   12.141%   $40.0904   $40.09   $40.10   $40.10  
  7 purchase totals = $904.77       $991.6801   $991.69   $991.65   $991.70